On Thu, 20 Dec 2018 21:51:48 -0000, % wrote:

On 2018-12-20 2:48 p.m., William Gothberg wrote:
On Thu, 20 Dec 2018 21:35:49 -0000, Rod Speed
wrote:



"William Gothberg" "William wrote in message
news On Thu, 20 Dec 2018 19:11:36 -0000, Rod Speed
wrote:

"William Gothberg" "William wrote in message
news On Thu, 20 Dec 2018 09:36:02 -0000, Jon Fairbairn
wrote:

"William Gothberg" "William writes:
Agreed. All I can detect (with my digital camera) is that
one brand of LED light I have flickers about 5 times less
(not sure if it's smother or faster) than the others.

Try a longer exposure and move the light rapidly relative to the
camera.

I wonder, if I fed the lamps with mains voltage DC, simply a bridge
rectifier and a huge capacitor, they'd reduce their flicker.

Wont work at all if they use capacitor droppers and

I made a few of those to power LEDs to indicate the function of my
central
heating. I'm looking inside the flickery lamp just now (£15, 20W).
Without undoing the glue holding the PSU onto the inside of it, all I
can
see is probably: the mains going through a large bipolar cap, a tiny
resistor (to discharge it safely?), a bridge rectifier, another very
large
resister (to limit the LED current more accurately?), then a 400V 4..7uF
capacitor (which is bulged).

A capacitor dropper with a rectifier and smoothing capacitor after it?

Yep, that's what it is.

The one I made has no smoothing cap, just mains to cap to resistor to
bridge to LED.

Yeah, not need for one if you don't mind the 100Hz flicker.

It was just indicator LEDs to tell me what water circuit was running. 3
zones from the one boiler switched with valves.

Perhaps this bulged cap is why I'm getting flicker, I'll try
replacing it
tomorrow.

they very likely do because those are the only cheap
droppers for dropping such a large voltage.

Aren't miniature SMPS units pretty cheap?

Not as cheap as the cap and the bridge rectifier.

I just bought a 12V 6A SMPS for £4.50.

Yeah, I did too.

Designed for powering LEDs

Mine will run anything 12V. I currently use it to power a water pump..

It was sold for LEDs, presumably it will run anything provided I don't
exceed the 6A.

However I've noticed they scrimp on the caps (or cooling). Loads of
them get bulged caps after a while, in particular a 3A PSU I ran 2A of
LEDs 24/7 from, failed in 1 year. It kept cutting out - I discovered
the bulk capacitor had dried out. Same happened (over a longer period)
with two monitor PSUs.

The LEDs I use are all Hues and have their
own power supply with the led strips.

The one I mentioned above was for an insectocuter, I removed the flours
and ballast and fitted strips of UV LEDs instead.

- but I've looked inside it and it's definitely a switched mode, not a
capacitor dropper. Now this flickery LED lamp I'm looking inside, it's
about 20W, so 12V at 2A is all that's required, it could have had an
SMPS
in it similar to the one I just described.

Yeah, but the cap and bridge are cheaper.

Well I've got 9W £4 strips with a switched mode PSU in them, so they
can't cost that much.

I'm now looking inside one of the better LED lamps (the non-flickery
model). It has a basic SMPS inside it. They're 9W and £4 each for the
whole lamp. I'm sure it's more than just a standard SMPS though,
because
when some LEDs fail short circuit (it has about 40 in series), the
voltage
coming from the PSU drops, to maintain the correct current for the
remaining good LEDs.

Yeah, its best to drive leds in constant current mode.

I'm surprised that the LEDs always fail short circuit, new type of LED
designed to do this?

And I think the LED failures are due to heat. I now run them with the
diffuser covers off to let them be cooler. I get more light out of them
too, and I think they look better when you can see all the dots.

Very easy to try tho and see if it works.

Looks like it would help the better ones, but not the crap one.

In fact capacitor dropper ones wont work at all when fed DC.

Agreed.

Better (as I only have a few crap ones) to stick a bigger smoothing cap
inside those.

Yep as long as it will fit.

They're huge inside, massive space. "Corn on the cob LED lights"
they're called. I could literally fit a cap about 50 times the size of
the one that's in it. It's probably enough smoothing with the original
size, I can't remember if it flickered when I bought it. But clearly
the cap was overworked as it failed, so I'll fit something larger so it
lasts longer this time.

For the good ones, the only problem I can foresee with the external
smoother, is overloading the lamp's bridge rectifier, as it will only be
conducting on two of the four diodes.

Should still be fine, most bridges in that situation are used
very conservitably and the diodes are rated for the initial
turn on surge current.

There's a current limiting resistor before them.

If I was to go ahead, I think I'd run one on the bench and check the
temperature of the diodes in normal operation. If they're not very warm
then they won't mind double the current.

Don't those diodes handle surges anyway? I mean a 3A diode will take
way more than that for a fraction of a second. It's the heat that kills
them. So why don't they just fit what they need to instead of bigger ones?

trimmers , you need trimmers

An adjustable diode? I'm quite sure you know nothing about what you're talking.